Electroless plating is a commonly used method for introducing a metal coating onto an object. To coat an object by electroless plating, a metal compound is placed in solution and the elemental metal is subsequently deposited via a chemical reaction. Electroless plating may be used to provide a highly uniform coating of a metal such as nickel, copper, silver, gold, platinum, or palladium on an item. Electroless plating is frequently used in the electronics industry, for example, in the processing of semiconductor wafers.
With time and use, an electroless plating solution will become exhausted and/or contaminated with by-products of the plating process, necessitating its replacement. Spent plating solutions, however, contain metal compounds, with their environmental considerations. Spent plating solutions can also tend to evolve a significant amount of hydrogen gas, presenting an explosion and fire hazard. As a result, a variety of methods have been devised to treat spent plating solutions.
U.S. Pat. No. 6,391,209, the disclosure of which is incorporated herein by reference, describes a number of prior methods for the treatment of spent plating solutions. These include treatment of the solution with an oxidizing agent such as hydrogen peroxide. Another method includes the chemical reduction of the metal and subsequent precipitation of organic complexing agents. Plating solutions may also be treated by exposure to ozone, ultraviolet light, or hydrogen peroxide, or a combination thereof.
U.S. Pat. No. 5,730,856, the disclosure of which is also incorporated herein by reference, describes a method for treating electroless plating solutions by electrolytic oxidation and simultaneous vibration and fluidization by an oscillating stirrer.
Electrochemical cells have also been used to remove metals from metal containing solutions such as electroless plating solutions. U.S. Pat. No. 6,162,333 to Lemon et al., the disclosure of which is incorporated herein by reference, describes such a cell.